There are various situations in which an actual road course may deviate, e.g. laterally, from an expected road course based upon the path of the road segment(s) of an electronic map representing the road. One common cause of a lateral road course deviation is roadworks. For example, where road works are affecting a lane or lanes of a road segment in a given direction of travel, vehicles may be forced to travel along a lane which usually forms part of the opposite carriageway, or along a hard shoulder. In either case, the actual road course followed in the given direction of travel will exhibit a lateral deviation from the expected course of travel according to the electronic map data representing the road.
Identification of the existence of a so-called (lateral) deviation or offset of a road course is useful for a number of reasons. A deviation may often have an adverse impact on traffic flow along the road. The identification of deviations of road course may therefore be useful in providing more accurate traffic information, and obtaining more accurate travel time estimates for routes. Travel along a road stretch incorporating a deviation may also necessitate greater attention by a driver, and it is useful therefore to identify affected stretches in order to provide advance warning to the driver, enhancing safety and/or to allow the driver to be guided appropriately in their navigation through the affected stretch.
It is known in current traffic information systems to consider traffic flow on different navigable stretches, and identify areas where flow is lower than might be expected. However, such methods do not consider the underlying cause of any reduction in flow, or provide a way of determining whether a deviation in road course is involved. In other arrangements, traffic messages may be received, e.g. from a third party, using a suitable distribution system, such as in the form of TMC (traffic message channel) messages. Such messages may indicate a stretch upon which traffic flow is affected by road works, but do not indicate any temporary deviation in course of the road as a result of the road works.
The Applicant has realised that there is a need for methods and systems for determining deviations in the course of navigable stretches.